Local tentative bonding method to maintain alignment accuracy in bonding process using resin as an adhesive material

The authors proposed a novel method to maintain the alignment accuracy in the wafer‐bonding process, which uses a resin as an adhesive material. Recently, the resin has received attention as an adhesive material for wafer bonding in microelectromechanical system device fabrication because of its multiple advantageous material properties. However, because of its inherent material viscosity, the alignment accuracy cannot be easily maintained, particularly when two wafers are bonded with a thick resin after alignment. To solve this problem, they proposed a local tentative bonding method. After aligning the two wafers, they irradiated the adhesive resin layer between the wafers using a near‐infrared (NIR) spotlight (wavelength = 1020 nm), which is transparent to Si wafers. Using several NIR irradiation spots aimed at the resin layer after aligning the wafers, the resin layer was bonded locally and tentatively, which was sufficiently secure to avoid wafer shifting in the subsequent process. The local tentative bonded areas acted as anchors, which held the wafers during the bonding process. They performed experiments to demonstrate the effectiveness of their method using resins, such as polyimide, benzocyclobutene and SU‐8. Consequently, they achieved an alignment accuracy <5 µm, which is a significant improvement compared with the typical bonding results.